Rejected gas recovery in gas oil separation plants

ABSTRACT

Rejected gas recovery in gas-oil separation plants (GOSPs) is implemented. A gas phase is flowed from a GOSP to a central gas plant through a first gas flow pathway at a first flow pressure. Gas from a gas reservoir is flowed through a second gas flow pathway at a second flow pressure. The first gas flow pathway is separate from the second gas flow pathway. While flowing the gas phase through the first gas flow pathway, a decrease in the first flow pressure below a threshold flow pressure is determined. In response, a gas-gas ejector, which is fluidically coupled to the first gas flow pathway and the second gas flow pathway, is operated to drive a flow of the gas phase to the central gas plant using gas from the gas reservoir as a motive gas.

TECHNICAL FIELD

This disclosure relates to managing gas phases obtained from gas oilseparation plants (GOSPs).

BACKGROUND

Hydrocarbons (e.g., oil product, natural gas, combinations of them)entrapped in subsurface reservoirs are raised to the surface (i.e.,produced) through wellbores formed from the surface to the subsurfacereservoirs through a subterranean zone (e.g., a formation, a portion ofa formation or multiple formations). Often, the produced hydrocarbonsare multiphase fluids that include a liquid phase and a gas phase. Theliquid phase can include the oil product and formation water. Inoperation, the multiphase hydrocarbons are flowed to GOSPs forseparation into their individual phases. In addition, the liquid phaseis separated into oil product and formation water. The oil product istransported to a stabilization plant for further treatment. Theformation water is injected back into the subterranean zone. The gasphase is transported to a central gas plant for further processing.Portions of the gas phase that cannot be transported to the central gasplant are rejected by flaring those portions using a flare system.

SUMMARY

This disclosure describes technologies relating to the rejected gasrecovery in GOSPs.

Certain aspects of the subject matter described here can be implementedas a gas flow system that includes a GOSP configured to separatemultiphase hydrocarbon into a gas phase and a liquid phase. A first gasflow pathway is fluidically coupled to the GOSP and configured toreceive the gas phase from the GOSP and to flow the gas phase to acentral gas plant at a first flow pressure. A second gas flow pathway isfluidically coupled to a gas reservoir and configured to flow gas fromthe gas reservoir to the central gas plant at a second flow pressuregreater than the first flow pressure. A gas-gas ejector is fluidicallycoupled to the first gas flow pathway and the second gas flow pathway.The gas-gas ejector is configured to drive gas flow using the gas fromthe gas reservoir as a motive gas. A controller is operatively coupledto the GOSP and the gas-gas ejector. The controller includes one or morecomputer systems and a computer-readable medium storing computerinstructions executable by the one or more computer systems to performoperations. The operations include determining a decrease in the firstflow pressure below a threshold flow pressure. In response todetermining the decrease in the first flow pressure below the thresholdflow pressure, the operations include operating the gas-gas ejector tooperate to drive a flow of the gas phase to the central gas plant usinggas from the gas reservoir as a motive gas.

An aspect combinable with any other aspect includes the followingfeatures. The system includes a gas compressor fluidically coupled tothe first gas flow pathway. The gas compressor is configured to flow thegas phase to the central gas plant at the first flow pressure. Todetermine the decrease in the first flow pressure below the thresholdflow pressure, a change in normal operation of the gas compressor isdetermined.

An aspect combinable with any other aspect includes the followingfeatures. A third gas flow pathway is fluidically coupled to the secondgas flow pathway and to a motive gas inlet of the gas-gas ejector. Afirst flow control valve is fluidically coupled to the third gas flowpathway and operatively coupled to the controller. To operate thegas-gas ejector, opening and closing of the first flow control valve iscontrolled.

An aspect combinable with any other aspect includes the followingfeatures. In an open state, the first flow control valve is configuredto divert a portion of the gas from the gas reservoir to the motive gasinlet of the gas-gas ejector. In a closed state, the flow control valveis configured to cease flow of the portion of the gas from the gasreservoir to the motive gas inlet of the gas-gas ejector.

An aspect combinable with any other aspect includes the followingfeatures. A fourth gas flow pathway is fluidically coupled to the firstgas flow pathway and to a driven gas inlet of the gas-gas ejector. Asecond flow control valve is fluidically coupled to the fourth gas flowpathway and operatively coupled to the controller. To operate thegas-gas ejector, opening and closing of the second flow control valve iscontrolled.

An aspect combinable with any other aspect includes the followingfeatures. In an open state, the second flow control valve is configuredto divert the gas phase from flowing to the central gas plant to flowingto the driven gas inlet of the gas-gas ejector. In a closed state, thesecond flow control valve is configured to divert the gas phase fromflowing to the driven gas inlet of the gas-gas ejector to flowing to thecentral gas plant.

Certain aspects of the subject matter described here can be implementedas a method. A gas phase is flowed from a GOSP to a central gas plantthrough a first gas flow pathway at a first flow pressure. Gas from agas reservoir is flowed through a second gas flow pathway at a secondflow pressure. The first gas flow pathway is separate from the secondgas flow pathway. While flowing the gas phase through the first gas flowpathway, a decrease in the first flow pressure below a threshold flowpressure is determined. In response, a gas-gas ejector, which isfluidically coupled to the first gas flow pathway and the second gasflow pathway, is operated to drive a flow of the gas phase to thecentral gas plant using gas from the gas reservoir as a motive gas.

An aspect combinable with any other aspect includes the followingfeatures. A gas compressor, fluidically coupled to the first gas flowpathway, flows the gas phase to the central gas plant at the first flowpressure. The decrease in the first flow pressure below the thresholdflow pressure is determined by determining a change in normal operationof the gas compressor.

An aspect combinable with any other aspect includes the followingfeatures. The normal operation of the gas compressor includes anoperation at a maximum flow pressure at which the gas compressor israted to operate. To determine the change in the normal operation, it isdetermined that the gas compressor is operating at a flow pressuredifferent from the maximum flow pressure.

An aspect combinable with any other aspect includes the followingfeatures. To operate the gas-gas ejector, a first flow control valve,which controls flow through a third gas flow pathway fluidically coupledto the second flow pathway and to a motive gas inlet of the gas-gasejector is opened, to flow a portion of the gas from the gas reservoirto the motive gas inlet of the gas-gas ejector.

An aspect combinable with any other aspect includes the followingfeatures. To operate the gas-gas ejector, a second flow control valve,which controls flow through a fourth gas flow pathway fluidicallycoupled to the first gas flow pathway and to a driven gas inlet of thegas-gas ejector, is opened to divert the gas phase from flowing to thecentral gas plant to flowing to the driven gas inlet of the gas-gasejector.

An aspect combinable with any other aspect includes the followingfeatures. While operating the gas-gas ejector, a flow pressure throughthe first gas flow pathway is periodically monitored. In response toperiodically monitoring the flow pressure, it is determined that theflow pressure of the gas phase exceeds the threshold flow pressure. Inresponse to determining that the flow pressure of the gas phase exceedsthe threshold flow pressure, the gas phase is flowed to the central gasplant while avoiding flow of the gas phase through the gas-gas ejector.

Certain aspects of the subject matter described here can be implementedas a non-transitory computer-readable medium storing instructionsexecutable by one or more computer systems to perform operations. Theoperations include receiving signals representing flow pressure of a gasphase flowing through a first gas flow pathway from a GOSP to a centralgas plant. While the gas phase is flowed to the central gas plant, gasfrom a gas reservoir is flowed through a second gas flow pathway from agas reservoir to the central gas plant. At a first time instant, it isdetermined that the flow pressure is less than a threshold flowpressure. In response, control signals are transmitted to operate agas-gas ejector fluidically coupled to the first gas flow pathway andthe second gas flow pathway, to drive a flow of the gas phase to thecentral gas plant using gas from the gas reservoir as a motive gas.

An aspect combinable with any other aspect includes the followingfeatures. A third gas flow pathway fluidically couples the second gasflow pathway to a motive gas inlet of the gas-gas ejector. A first flowcontrol valve fluidically couples to the third gas flow pathway. Totransmit control signals to operate the gas-gas ejector, control signalsare transmitted to open the first flow control valve to divert a portionof the gas from the gas reservoir to the motive gas inlet of the gas-gasejector.

An aspect combinable with any other aspect includes the followingfeatures. A fourth gas flow pathway fluidically couples the first gasflow pathway to a driven gas inlet of the gas-gas ejector. A second flowcontrol valve fluidically couples the first gas flow pathway to a drivengas inlet of the gas-gas ejector. A second flow control valvefluidically couples to the fourth gas flow pathway. To transmit controlsignals to operate the gas-gas ejector, control signals are transmittedto open the second flow control valve to divert the gas phase fromflowing to the central gas plant to flowing to the driven gas inlet ofthe gas-gas ejector.

An aspect combinable with any other aspect includes the followingfeatures. At a second time instant after the first time instant, it isdetermined that the flow pressure is greater than the threshold flowpressure. In response, control signals are transmitted to close thefirst flow control valve and the second flow control valve.

An aspect combinable with any other aspect includes the followingfeatures. To receive signals representing flow pressure of the gas phaseflowing through the first gas flow pathway, signals are received frompressure sensors fluidically coupled to the first gas flow pathway.

Certain aspects of the subject matter described here can be implementedas a gas flow system. The system includes multiple GOSPs, eachconfigured to separate multiphase hydrocarbon into a gas phase and aliquid phase. Multiple first gas flow pathways are fluidically coupledto the respective multiple GOSPs. Each first gas flow pathway isconfigured to receive the gas phase from a respective GOSP of themultiple GOSPs at a respective first flow pressure. A second gas flowpathway is fluidically coupled to each first gas flow pathway of themultiple first gas flow pathways. The second gas flow pathway isconfigured to flow the gas phase received from each first gas flowpathway to a central gas plant at a second flow pressure greater thaneach first flow pressure in each first gas flow pathway. A gas-gasejector is fluidically coupled to one of the multiple first gas flowpathway and to the second gas flow pathway. The gas-gas ejector isconfigured to drive gas flow using the gas phase flowed through thesecond gas flow pathway as a motive gas. A controller is operativelycoupled to the GOSP and the gas-gas ejector. The controller includes oneor more gas systems and a computer-readable medium storing computerinstructions executable by the one or more computer systems to performoperations. The operations include determining a decrease in the firstflow pressure of the one of the multiple first gas flow pathways towhich the gas-gas ejector is coupled to below a threshold flow pressure.The operations include, in response, operating the gas-gas ejector tooperate to drive a flow of the gas phase from the one of the multiplefirst gas flow pathways to the central gas plant using the gas phase inthe second gas flow pathway as a motive gas.

An aspect combinable with any other aspect includes the followingfeatures. A gas compressor is fluidically coupled to the one of themultiple first gas flow pathways. The gas compressor is configured toflow the gas phase to the second gas flow pathway at the first flowpressure. To determine the decrease in the first flow pressure below thethreshold flow pressure, a change in normal operation of the gascompressor is determined.

An aspect combinable with any other aspect includes the followingfeatures. The normal operation of the gas compressor includes anoperation at a maximum flow pressure at which the gas compressor israted to operate. To determine the change in the normal operation, it isdetermined that the gas compressor is operating at a flow pressuredifferent from the maximum flow pressure.

An aspect combinable with any other aspect includes the followingfeatures. A third gas flow pathway is fluidically coupled to the secondgas flow pathway and to a motive gas inlet of the gas-gas ejector. Afirst flow control valve is fluidically coupled to the third gas flowpathway and operatively coupled to the controller. To operate thegas-gas ejector, opening and closing of the first flow control valve iscontrolled.

An aspect combinable with any other aspect includes the followingfeatures. The first flow control valve, in an open state, is configuredto divert a portion of the gas phase from the second gas flow pathway tothe motive gas inlet of the gas-gas ejector. In a closed state, thefirst flow control valve is configured to cease flow of the portion ofthe gas phase from the second gas flow pathway to the motive gas inletof the gas-gas ejector.

An aspect combinable with any other aspect includes the followingfeatures. A fourth gas flow pathway is fluidically coupled to the one ofthe multiple first gas flow pathways and to a drive gas inlet of thegas-gas ejector. A second flow control valve is fluidically coupled tothe fourth gas flow pathway and operatively coupled to the controller.To operate the gas-gas ejector, opening and closing of the second flowcontrol valve is controlled.

An aspect combinable with any other aspect includes the followingfeatures. The second flow control valve, in an open state, is configuredto divert the gas phase from flowing to the second gas flow pathway toflowing to the driven gas inlet of the gas-gas ejector. In a closedstate, the second flow control valve is configured to divert the gasphase from flowing to the driven gas inlet of the gas-gas ejector toflowing to the second gas flow pathway.

Certain aspects of the subject matter described here can be implementedas a method. A gas phase is flowed from a first GOSP through a first gasflow pathway to a second gas flow pathway at a first flow pressure. Thegas phase from the second gas flow pathway is flowed to a central gasplant at a second flow pressure greater than the first flow pressure.The second gas flow pathway receives a gas phase from a second GOSP.While flowing the gas phase through the first gas flow pathway, adecrease in the first flow pressure below a threshold flow pressure isdetermined. In response, a gas-gas ejector, fluidically coupled to thefirst gas flow pathway and the second gas flow pathway, is operated todrive a flow of the gas phase to the central gas plant using the gasphase flowed through the second gas flow pathway at the second flowpressure as a motive gas.

An aspect combinable with any other aspect includes the followingfeatures. A gas compressor, fluidically coupled to the first gas flowpathway, flows the gas phase to the second gas flow pathway at the firstflow pressure. To determine the decrease in the first flow pressurebelow the threshold flow pressure, a change in normal operation of thegas compressor is determined.

An aspect combinable with any other aspect includes the followingfeatures. Normal operation of the gas compressor includes an operationat a maximum flow pressure at which the gas compressor is rated tooperate. To determine the change in the normal operation, it isdetermined that the gas compressor is operating at a flow pressuredifferent from the maximum flow pressure.

An aspect combinable with any other aspect includes the followingfeatures. To operate the gas-gas ejector, a first flow control valvethat controls flow through a third gas flow pathway, fluidically coupledto the second gas flow pathway, and to a motive gas inlet of the gas-gasejector is opened to flow a portion of the gas phase from the second gasflow pathway to the motive gas inlet of the gas-gas ejector.

An aspect combinable with any other aspect includes the followingfeatures. To operate the gas-gas ejector, a second flow control valvethat controls flow through a fourth gas flow pathway, fluidicallycoupled to the first gas flow pathway, and to a driven gas inlet of thegas-gas ejector is opened to divert the gas phase from flowing to thesecond gas flow pathway to flowing to the driven gas inlet of thegas-gas ejector.

An aspect combinable with any other aspect includes the followingfeatures. While operating the gas-gas ejector, a flow pressure throughthe first gas flow pathway is periodically monitored. In response, it isdetermined that the flow pressure of the gas phase exceeds the thresholdflow pressure. In response to determining that the flow pressure of thegas phase exceeds the threshold flow pressure, the gas phase is flowedto the second gas flow pathway while avoiding flow of the gas phasethrough the gas-gas ejector.

An aspect combinable with any other aspect includes the followingfeatures. In response to determining that the flow pressure of the gasphase exceeds the threshold flow pressure, the gas is flowed from thesecond gas flow pathway to the central gas plant while avoiding flow ofthe gas from the second gas flow pathway through the gas-gas ejector.

Certain aspects of the subject matter described here can be implementedas a non-transitory computer-readable medium storing instructionsexecutable by the one or more computer systems to perform operations.The operations include receiving signals representing flow pressure of agas phase flowing through a first gas flow pathway from a first GOSP toa second gas flow pathway. While the gas phase is flowed from the firstgas flow pathway to the second gas flow pathway, a gas phase is flowedto the second gas flow pathway from a second GOSP. At a first timeinstant, it is determined that the flow pressure is less than athreshold flow pressure. In response, control signals are transmitted tooperate a gas-gas ejector, fluidically coupled to the first gas flowpathway and the second gas flow pathway, to drive a flow of the gasphase to the central gas plant using gas from the second gas flowpathway as a motive gas.

An aspect combinable with any other aspect includes the followingfeatures. A third gas flow pathway fluidically couples the second gasflow pathway to a motive gas inlet of the gas-gas ejector. A first flowcontrol valve fluidically couples to the third gas flow pathway. Totransmit control signals to operate the gas-gas ejector, control signalsare transmitted to open the first flow control valve to divert a portionof the gas from the second gas flow pathway to the motive gas inlet ofthe gas-gas ejector.

An aspect combinable with any other aspect includes the followingfeatures. A fourth gas flow pathway fluidically couples the first gasflow pathway to a driven gas inlet of the gas-gas ejector. A second flowcontrol valve fluidically couples to the fourth gas flow pathway. Totransmit control signals to operate the gas-gas ejector, control signalsare transmitted to open the second flow control valve to open the secondflow control valve to divert the gas phase from flowing to the secondgas flow pathway to flowing to the driven gas inlet of the gas-gasejector.

An aspect combinable with any other aspect includes the followingfeatures. At a second time instant after the first time instant, it isdetermined that the flow pressure is greater than the threshold flowpressure. In response, control signals are transmitted to close thefirst flow control valve and the second flow control valve.

An aspect combinable with any other aspect includes the followingfeatures. To receive signals representing flow pressure of the gas phaseflowing through the first gas flow pathway, signals are received frompressure sensors fluidically coupled to the first gas flow pathway.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an implementation of a gas flow system.

FIG. 2 is a flowchart of an example of a process of implementing the gasflow system of FIG. 1 .

FIG. 3 is a schematic diagram of a gas-gas ejector used in the gas flowsystem of FIG. 1 .

FIG. 4 is a schematic diagram of another implementation of a gas flowsystem.

FIG. 5 is a flowchart of an example of a process of implementing the gasflow system of FIG. 4 .

FIG. 6 is a schematic diagram of a gas-gas ejector used in the gas flowsystem of FIG. 4 .

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

A GOSP implements high-pressure (HP) gas compressors to flow the gasphase separated from the multiphase hydrocarbons to the central gasplant where the gas phase is further processed. The central gas plantcan be far away (e.g., several hundred kilometers away) from the GOSP.The HP gas compressors can be rated to operate at gas flow pressuresneeded to flow the gas phase over the long distances that separated thecentral gas plant and the GOSP. However, in some instances, the HP gascompressors do not operate at the related gas flow pressures to flow thegas phase to the central gas plant. For example, the operating gas flowpressure in the GOSP can be less than the related gas flow pressure ofthe HP gas compressor when the gas compressor is either starting up orshutting down (e.g., for preventative maintenance). In another example,the flow rate of the gas phase through the GOSP declines over timeresulting in a lower gas flow rate, compared to the related gas flowrate, through the HP gas compressors. In such instances, the HP gascompressor will be put on a partially recycling more to prevent lowsuction flow rate, which can result in energy wastage. Also, in suchinstances, the gas phase that cannot be pumped by the HP gas compressoris treated as rejected gas, and is flowed to a flare system using whichthe rejected gases flared.

This disclosure describes techniques to minimize rejected gas thatcannot be pumped from the GOSP to the central gas plant due to areduction in gas flow pressure at which the HP gas compressors operate.The techniques described in this disclosure utilize available energyfrom other sources to provide gas flow pressure to flow the gas phase tothe central gas plant, rather than implementing new sources that wouldadd to energy usage. By implementing the techniques described here, avolume of gas phase that is recovered for processing in the central gasplant can be increased. Correspondingly, the volume of gas phase that isflared to the atmosphere can be decreased. Power required to operate theHP gas compressors in GOSPs, and, by extension, to operate the GOSPsthemselves can be optimized. Overall, GOSPs can be operated moreefficiently.

FIG. 1 is a schematic diagram of an implementation of a gas flow system100. The gas flow system 100 includes a GOSP 102 that can separatemultiphase hydrocarbon into a gas phase and a liquid phase. The GOSP 102can receive the multiphase hydrocarbon from a well system (not shown).The gas flow system 100 includes multiple gas flow pathways each ofwhich can be implemented as a pipeline, flowline or other tubularsthrough which gas can be flowed and to which gas flow equipment (e.g.,gas flow meters, pressure gauges, pumps, compressors or other gas flowequipment) can be fluidically coupled. In some implementations, the gasflow system 100 includes a first gas flow pathway 104 fluidicallycoupled to the GOSP 102. The first gas flow pathway 104 can receive thegas phase from the GOSP 102 and flow the gas phase to a central gasplant 106 at a first flow pressure.

In some implementations, the gas flow system 100 includes a gascompressor 108, an HP gas compressor, fluidically coupled to the firstgas flow pathway 104. The gas compressor 108 is configured to pump thegas phase to the central gas plant at the first flow pressure. The gascompressor 108 is rated to operate at least at the first flow pressure.That is, the gas compressor 108 is designed and constructed such thatthe gas compressor 108 operates at optimal efficiency when the flowpressure of gas being pumped by the gas compressor 108 is at least atthe first flow pressure. At flow pressures below the rated pressure, thegas compressor 108 operates inefficiently and may not be able to pumpall of the gas phase received from the GOSP 102 to the central gas plant106.

The central gas plant 106 includes multiple gas processing facilityunits, each configured to process gas received from a respective source.For example, the central gas plant 106 includes a GOSP gas processingfacility 109 fluidically coupled to the first gas flow pathway 104. TheGOSP gas processing facility 109 receives the gas phase from the GOSP102 through the first gas flow pathway 104, and processes the gas phase(e.g., prepares the gas phase for shipping to sales destinations).

In some implementations, the central gas plant 106 includes a reservoirgas processing facility 110 that receives gas from a gas reservoir 112.For example, a gas well (not shown) is formed from the surface to asubsurface gas reservoir to produce natural gas entrapped in the gasreservoir 112. A second gas flow pathway 114 is fluidically coupled tothe gas reservoir 112 (e.g., the gas well) and to the reservoir gasprocessing facility 110 at the central gas plant 106. Gas from the gasreservoir 112 is produced at a high pressure, and the flow of the gas tothe second gas flow pathway 114 is controlled by a wellhead choke valve(not shown) installed at the gas well and, in some instances, otherwells fluidically installed on the second gas flow pathway 114. The gasflows through the second gas flow pathway 114 from the gas reservoir 112to the central gas plant 106 at a second flow pressure that is greaterthan the first flow pressure. That is, a pressure at which the gas flowsfrom the gas reservoir 112 to the central gas plant 106 is greater thanthe pressure at which the HP gas compressor 108 pumps the gas phase fromthe GOSP 102 to the central gas plant 106.

When the flow rate of the gas phase through the GOSP 102 is optimal orwhen the HP gas compressor 108 operates at or above its rated flowpressure, the gas phase and the gas from the gas reservoir 112 can flowthrough the first gas flow pathway 104 and the second gas flow pathway114, respectively, independent of each other. That is, under the optimaloperating conditions described in this paragraph, the flow of the gasphase from the GOSP 102 is unaffected by the flow of the gas from thegas reservoir 112. However, in instances such as those described above,the flow rate of the gas phase through the GOSP 102 is not optimal orthe HP gas compressor 108 does not operate at or above its rated flowpressure. In such instances, as described above, a portion of the gasphase may be rejected by flaring the portion to the atmosphere through aflare system (not shown).

To recover such portions of the gas phase and to avoid such flaring, agas-gas ejector 116 can be implemented. The gas-gas ejector 116 isfluidically coupled to the first gas flow pathway 104 and the second gasflow pathway. The gas-gas ejector 116 is configured to drive gas flowusing the gas from the gas reservoir 112 as a motive gas. The gas-gasejector 116 uses high-pressure gas (e.g., gas from the gas reservoir112) to drive flow of low-pressure gas (e.g., gas phase from the GOSP102). The gas-gas ejector 116 uses a converging nozzle to increase gasvelocity to transform high static pressure into velocity pressure. Thisconversion results in a low-pressure zone that provides the motive forceto and claim a site fluid; in this case, the gas phase from the GOSP102. The high-pressure gas and the low-pressure gas mix, and the mixedgas flows through a diffuser section that includes a diverging nozzle,which reduces the velocity and increases the pressure, therebyre-compressing the mixed gas.

In some implementations, the gas-gas ejector 116 is implemented onlywhen the flow pressure through the first gas flow pathway 104 fallsbelow a threshold flow pressure. For example, the threshold flowpressure can be the minimum flow pressure at which the HP gas compressor108 is rated to operate or the minimum flow pressure at which the gasphase needs to flow through the GOSP 102. In another example, thethreshold flow pressure can be the minimum flow pressure below which atleast a portion of the gas phase needs to be rejected via the flaresystem.

In some implementations, the gas flow system 100 includes a controlleroperatively coupled to the components of the gas flow system 100, e.g.,the GOSP 102, the gas flow pathways, the gas-gas ejector 116, to name afew. Also, the gas flow system 100 includes sensors (e.g., pressuregauges, flowmeters, combinations of them) fluidically coupled to the gasflow pathways that can sense flow parameters (e.g., flow pressure, flowvelocity, other flow parameters) and can generate and transmit signals(e.g., electrical, electronic, the top signals) that represent thesensed flow parameters. The controller 118 includes one or more computersystems 120 and a computer-readable medium 122 storing instructionsexecutable by the one or more computer systems 120 to perform operationsdescribed in this disclosure. The controller 118 can receive the signalsthat represent the sensed flow parameters from the various sensorsdeployed in the gas flow system 100.

As described below with reference to FIG. 2 , the controller 118 cancause the gas-gas ejector 116 to be deployed only when the signalsreceived from the sensors indicate that the flow pressure through thefirst gas flow pathway 104 is less than the threshold flow pressure. Forexample, the controller 118 can implement operations to determine adecrease in the first flow pressure below the threshold flow pressure.In response to determining the decrease in the first flow pressure belowthe threshold flow pressure, the controller 118 can cause the gas-gasejector 116 to operate to drive a flow of the gas phase to the centralgas plant 106 using gas from the gas reservoir 112 as a motive gas.

FIG. 2 is a flowchart of an example of a process 200 of implementing thegas flow system of FIG. 1 . In some implementations, the process 200 canbe performed by the controller 118. At 202, the controller 118periodically monitors flow pressure in the first gas flow pathway 104through which gas phase is flowed from the GOSP 102 to the central gasplant 106. For example, the controller 118 receives signals representingflow pressure of the gas flow flowing through the first gas flow pathway104 from sensors fluidically coupled to the first gas flow pathway 104.While the gas phase is being flowed to the central gas plant 106 fromthe GOSP 102, gas from the gas reservoir 112 is, in parallel, beingflowed through the second gas flow pathway 114 to the central gas plant106.

In some implementations, the controller 118 stores, e.g., in thecomputer-readable medium 122, a value representing the threshold flowpressure. The threshold flow pressure value can be chosen based on therated pressure at which the HP gas compressor 108 can optimally pump thegas phase through the first gas flow pathway 104 from the GOSP 102 tothe central gas plant 106. The controller 118 can periodically (e.g., ata certain frequency such as once per second, once every 10 seconds, onceevery seconds, once a minute, and so on) compare flow pressure receivedfrom the sensors to the stored threshold flow pressure. As long as thecontroller 118 determines that the received flow pressure is greaterthan or equal to the threshold flow pressure, the gas-gas ejector 116 isnot deployed, and flow of the gas phase through the first gas flowpathway 104 is unaffected by flow of the gas through the second gas flowpathway 114.

At 204, the controller 118 determines that flow pressure through thefirst gas flow pathway 104 is below the threshold flow pressure. Forexample, the controller 118 compares the flow pressure received from thesensors to the stored threshold flow pressure, and determines that theformer is less than the latter. At 206, in response, the controller 118transmits control signals to operate the gas-gas ejector 116 to driveflow of the gas phase through the first gas flow pathway 104 to thecentral gas plant 106 using the gas from the gas reservoir 114 as amotive gas.

FIG. 3 is a schematic diagram of the gas-gas ejector 116 with thefluidic connections to the components of the gas flow system 100. Thegas flow system 100 includes a third gas flow pathway 302 thatfluidically couples the second gas flow pathway 114 to a motive gasinlet 304 of the gas-gas ejector 116. High-pressure gas (in this case,gas from the gas reservoir 112) flows into the motive gas inlet 304. Afirst flow control valve 306 is fluidically coupled to the third gasflow pathway 302. The first flow control valve 306 controls (i.e.,permits or prevents) flow of the gas through the third gas flow pathway302 from the second gas flow pathway 114 to the motive gas inlet 304.The first flow control valve 306 is operatively coupled to thecontroller 118, and can open or close based on and in response tocontrol signals received from the controller 118. In response to thecontroller 118 transmitting control signals to the first flow controlvalve 306, the first flow control valve 306 opens, thereby diverting aportion of the gas from the gas reservoir 112 to the motive gas inlet304.

The gas flow system 100 includes a fourth gas flow pathway 308 thatfluidically couples the first gas flow pathway 104 to a driven gas inlet310 of the gas-gas ejector 16. Low pressure gas (in this case, gas fromthe GOSP 102 when the HP gas compressor 108 is operating below thethreshold flow pressure) flows into the driven gas inlet 310. A secondflow control valve 312 controls (i.e., permits or prevents) flow of thegas through the fourth gas flow pathway 308 from the first gas flowpathway 104 to the driven gas inlet 310. The second flow control valve312 is operatively coupled to the controller 118, and can open or closebased on and in response to control signals received from the controller118. In response to the controller 118 transmitting control signals tothe second flow control valve 312, the second flow control valve 312opens, thereby diverting the gas phase from the GOSP 102 to the drivengas inlet 310.

In some implementations, the gas flow system 100 can include anotherflow control valve 314 between the first gas flow pathway 104 and thecentral gas plant 106, specifically the GOSP gas processing facility109. The flow control valve 314 is also operatively coupled to thecontroller 118, and can open or close based on and in response tocontrol signals received from the controller 118. When the flow controlvalve 312 is open, the flow control valve 314 is closed. Under thisarrangement, when the gas-gas ejector 116 is implemented, all gas phasefrom the GOSP 102 is flowed through the driven gas inlet 310. In otherwords, no gas phase is flowed directly to the central gas plant 106while avoiding the gas-gas ejector 116. Also under this arrangement, thegas flow pathway 316 is operatively coupled to the outlet 318 of thegas-gas ejector 116 to flow the gas mixture (i.e., mixture of the gasphase from the GOSP 102 and the gas from the gas reservoir 112) exitingthe gas-gas ejector 316 back to the first gas flow pathway 104 for finaldelivery to the central gas plant 106.

The earlier descriptions describe a scenario at a time instant in whichthe gas-gas ejector 116 is implemented because the flow pressure of thegas phase through the first gas flow pathway 104 has fallen below athreshold flow pressure. As described earlier, such pressure drop canoccur, for example, because the HP gas compressor 108 is starting up orshutting down or is malfunctioning. Such pressure drop can also occurwhen the flow pressure of the gas phase flowing through the GOSP 102drops. At a later time instant, the flow pressure of the gas phasethrough the first gas flow pathway 104 can increase to at or above thethreshold flow pressure. Such pressure increase can occur, for example,because the HP gas compressor 108 is running optimally at the maximumflow pressure at which the HP gas compressor 108 is rated to operate.Such pressure increase can also occur because the gas phase is flowingoptimally through the GOSP 102. In such scenarios, the gas-gas ejector116 is no longer needed.

In response to determining that the flow pressure of the gas phase flowthrough the first gas flow pathway 104 is at or above the threshold flowpressure, the controller 118 can transmit signals to close the firstflow control valve 306, close the second flow control valve 312 and openthe flow control valve 314. In response, the portion of the gas from thegas reservoir 112, which was previously diverted to flow through thethird gas flow pathway 302, can resume flowing entirely through thesecond gas flow pathway 114 to the central gas plant 106. Also, the gasphase from the GOSP 102, which was previously diverted to flow throughthe fourth gas flow pathway 308, can resume flowing entirely through thefirst gas flow pathway 104 to the central gas plant 106. In this manner,by periodically monitoring the pressure in the first gas flow pathway104, the gas flow system 100 can implement the gas-gas ejector 116 asneeded.

FIG. 4 is a schematic diagram of another implementation of a gas flowsystem 400. The gas flow system 400 includes a network of multiple GOSPs(e.g., GOSPs 402A-H or fewer or more GOSPs), each of which can separatemultiphase hydrocarbon into a gas phase and a liquid phase. Each GOSPcan receive the multiphase hydrocarbon from a well system (not shown) orfrom multiple well systems (not shown). The gas flow system 400 includesmultiple gas flow pathways each of which can be implemented as apipeline, flowline or other tubulars through which gas can be flowed andto which gas flow equipment (e.g., gas flow meters, pressure gauges,pumps, compressors or other gas flow equipment) can be fluidicallycoupled. In some implementations, each GOSP in the gas flow system 400includes a respective first gas flow pathway (e.g., first gas flowpathway 404 a for GOSP 402A, first gas flow pathway 404B for GOSP 402Band similarly first gas flow pathways 404C-404H for GOSPs 402C-402H,respectively) fluidically coupled to the GOSP.

Each first gas flow pathway can receive the gas phase from a respectiveGOSP and flow the gas phase to a second gas flow pathway 406 at arespective first flow pressure. The second gas flow pathway 406 receivesthe gas phase from each first gas flow pathway and collectively flowsthe gas faces from the network of multiple GOSPs to a central gas plant408 (similar to the central gas plant 106 of FIG. 1 ). The flow pressureof the gas phase through each respective first gas flow pathway can bedifferent. The flow pressure of the gas phase through the second gasflow pathway 406 can be greater than the flow pressure through any ofthe individual first gas flow pathways.

In some implementations, the gas flow system 400 includes multiple gascompressors, e.g., each being an HP gas compressor similar to the gascompressor 108 of FIG. 1 . Each first gas flow pathway originating fromeach GOSP can include a respective gas compressor (e.g., gas compressor410A fluidically coupled to the first gas flow pathway 404A of the GOSP402A). Each gas compressor is configured to pump the gas phase from therespective GOSP to the second gas flow pathway 406 at a respective firstflow pressure. Each gas compressor is rated to operate at least at thefirst flow pressure. That is, the gas compressor 410A is designed andconstructed such that the gas compressor 410A operates at optimalefficiency when the flow pressure of gas being pumped by the gascompressor 410A is at least at the first flow pressure. At flowpressures below the rated pressure, the gas compressor 410A operatesinefficiently and may not be able to pump all of the gas phase receivedfrom the GOSP 402A to the second gas flow pathway 406.

The central gas plant 408 includes a gas processing facility unitconfigured to process gas received from the network of multiple GOSPs.Alternatively, the central gas plant 408 can include multiple gasprocessing facilities to which the gas phase received from the networkcan be distributed. In some implementations, the second gas flow pathway406 is fluidically coupled to the one or more gas processing facilityunits.

When the flow rate of the gas phase through a GOSP is optimal or whenthe HP gas compressor of the gas phase operates at or above its ratedflow pressure, all gas phase from the GOSP can be flowed to the secondgas flow pathway 4064 argument debris to the central gas plant 408.However, in instances such as those described above, the flow rate ofthe gas phase through the GOSP is not optimal or the HP gas compressordoes not operate at or above its rated flow pressure. In such instances,as described above, a portion of the gas phase may be rejected byflaring the portion to the atmosphere through a flare system (notshown).

To recover such portions of the gas phase and to avoid such flaring, agas-gas ejector 410 (similar to the gas-gas ejector 116 of FIGS. 1 and 3) can be implemented. The gas-gas ejector 410 is fluidically coupled tothe first gas flow pathway of the GOSP where the flow pressure is lessthan the threshold flow pressure. That is, the gas phase from such afirst gas flow pathway is flowed to a driven gas inlet of the gas-gasejector 410. The gas-gas ejector 410 is also fluidically coupled to thesecond gas flow pathway 406. That is, a portion of the gas phase fromthe second gas flow pathway 406 is flowed to a motive gas inlet of thegas-gas ejector for them. Similar to the gas-gas ejector 116 (FIGS. 1and 3 ), the gas-gas ejector 410 is configured to drive gas flow usingthe gas phase from the second gas flow pathway 406 as a motive gas. Thegas-gas ejector 116 uses high-pressure gas (e.g., gas phase from thesecond gas flow pathway 406) to drive flow of low-pressure gas (e.g.,gas phase from the GOSP operating below the threshold flow pressure).The gas-gas ejector 410 uses a converging nozzle to increase gasvelocity to transform high static pressure into velocity pressure. Thisconversion results in a low-pressure zone that provides the motive forceto and claim a site fluid; in this case, the gas phase from the GOSPoperating below the threshold flow pressure. The high-pressure gas andthe low-pressure gas mix, and the mixed gas flows through a diffusersection that includes a diverging nozzle, which reduces the velocity andincreases the pressure, thereby re-compressing the mixed gas.

In some implementations, the gas-gas ejector 410 is implemented onlywhen the flow pressure through any one of the first gas flow pathwaysfalls below a threshold flow pressure. For example, for the first gasflow pathway 404A, the threshold flow pressure can be the minimum flowpressure at which the HP gas compressor 410A is rated to operate or theminimum flow pressure at which the gas phase needs to flow through theGOSP 402A. In another example, the threshold flow pressure can be theminimum flow pressure below which at least a portion of the gas phasefrom the GOSP 402A needs to be rejected via the flare system.

In some implementations, the gas flow system 400 includes a controller412 (similar to the controller 118 of FIG. 1 ) operatively coupled tothe components of the gas flow system 400, e.g., each GOSP, each gasflow pathways, the gas-gas ejector 410, to name a few. Also, the gasflow system 400 includes sensors (e.g., pressure gauges, flowmeters,combinations of them) fluidically coupled to the gas flow pathways thatcan sense flow parameters (e.g., flow pressure, flow velocity, otherflow parameters) and can generate and transmit signals (e.g.,electrical, electronic, the top signals) that represent the sensed flowparameters. The controller 412 includes one or more computer systems 414and a computer-readable medium 416 storing instructions executable bythe one or more computer systems 414 to perform operations described inthis disclosure. The controller 412 can receive the signals thatrepresent the sensed flow parameters from the various sensors deployedin the gas flow system 400.

As described below with reference to FIG. 5 , the controller 412 cancause the gas-gas ejector 410 to be deployed only when the signalsreceived from the sensors indicate that the flow pressure through afirst gas flow pathway is less than the threshold flow pressure. Forexample, the controller 412 can implement operations to determine adecrease in the first flow pressure below the threshold flow pressure.In response to determining the decrease in the first flow pressure belowthe threshold flow pressure, the controller 412 can cause the gas-gasejector 410 to operate to drive a flow of the gas phase to the centralgas plant 408 using gas phases collected from the other GOSPs in thenetwork as a motive gas.

FIG. 5 is a flowchart of an example of a process 500 of implementing thegas flow system of FIG. 4 . In some implementations, the process 500 canbe performed by the controller 412. At 502, the controller 412periodically monitors flow pressure in each of the first gas flowpathways through which gas phase is flowed from the respective GOSP tothe central gas plant 408. For example, the controller 412 receivessignals representing flow pressure of the gas flow flowing through eachfirst gas flow pathway from sensors fluidically coupled to each firstgas flow pathway. As described above, gas phase from each GOSP is beingflowed through the respective first gas flow pathway to the second gasflow pathway 406.

In some implementations, the controller 412 stores, e.g., in thecomputer-readable medium 416, a value representing the threshold flowpressure. The threshold flow pressure value can be chosen based on therated pressure at which each HP gas compressor can optimally pump thegas phase through the respective first gas flow pathway from therespective GOSP to the central gas plant 408. The controller 412 canperiodically (e.g., at a certain frequency such as once per second, onceevery 10 seconds, once every 30 seconds, once a minute, and so on)compare flow pressure received from the sensors to the stored thresholdflow pressure. As long as the controller 412 determines that thereceived flow pressure is greater than or equal to the threshold flowpressure, the gas-gas ejector 410 need not be deployed, and flow of thegas phase through each first gas flow pathway is unaffected by flow ofthe gas through the second gas flow pathway 406.

At 504, the controller 118 determines that flow pressure through a firstgas flow pathway (e.g., first gas flow pathway 404H fluidically coupledto GOSP 402H) is below the threshold flow pressure. For example, thecontroller 412 compares the flow pressure received from the sensors tothe stored threshold flow pressure, and determines that the former isless than the latter. At 506, in response, the controller 412 transmitscontrol signals to operate the gas-gas ejector 410 to drive flow of thegas phase through the first gas flow pathway 404H to the central gasplant 408 using the gas phase from the second gas flow pathway 406 as amotive gas.

In some implementations of step 506, the controller 412 transmits analert (e.g., a visual signal, and audio signal, and electronic signal, adata signal or any combination of them) to an operator indicating thatthe flow pressure through the first gas flow pathway 404H is below thethreshold flow pressure. In response, the operator deploys the gas-gasejector 410 between the GOSP 404H and the GOSP that is immediatelyupstream or downstream of the GOSP 404H. in the present example, becausethe GOSP 404H is most downstream of all the other GOSPs in the network,the gas-gas ejector 410 is deployed between the GOSP 404H and thecentral gas plant 408. In an alternative scenario, if the controller 412had determined that the flow pressure through the first gas flow pathway404B was below the threshold flow pressure, then the operator woulddeploy the gas-gas ejector 410 at the GOSP 404A or the GOSP 404C.

FIG. 6 is a schematic diagram of the gas-gas ejector 410 with thefluidic connections to the components of the gas flow system 100. Thegas flow system 400 includes a third gas flow pathway 602 thatfluidically couples the second gas flow pathway 406 to a motive gasinlet 604 of the gas-gas ejector 410. High-pressure gas (in this case,gas phase from the second gas flow pathway 406) flows into the motivegas inlet 604. A first flow control valve 606 is fluidically coupled tothe third gas flow pathway 602. The first flow control valve 606controls (i.e., permits or prevents) flow of the gas through the thirdgas flow pathway 602 from the second gas flow pathway 406 to the motivegas inlet 604. The first flow control valve 606 is operatively coupledto the controller 412, and can open or close based on and in response tocontrol signals received from the controller 412. In response to thecontroller 412 transmitting control signals to the first flow controlvalve 606, the first flow control valve 606 opens, thereby diverting aportion of the gas phase from the second gas flow pathway 406 to themotive gas inlet 604.

The gas flow system 100 includes a fourth gas flow pathway 610 thatfluidically couples the first gas flow pathway 404H to a driven gasinlet 612 of the gas-gas ejector 16. Low pressure gas (in this case, gasfrom the GOSP 402H when the HP gas compressor is operating below thethreshold flow pressure) flows into the driven gas inlet 612. A secondflow control valve 614 controls (i.e., permits or prevents) flow of thegas through the fourth gas flow pathway 610 from the first gas flowpathway 404H to the driven gas inlet 612. The second flow control valve614 is operatively coupled to the controller 412, and can open or closebased on and in response to control signals received from the controller412. In response to the controller 412 transmitting control signals tothe second flow control valve 614, the second flow control valve 614opens, thereby diverting the gas phase from the GOSP 404H to the drivengas inlet 612.

In some implementations, the gas flow pathway 406 is operatively coupledto the outlet 618 of the gas-gas ejector 410 to flow the gas mixture(i.e., mixture of the gas phase from the GOSP 404H and the gas from thesecond gas flow pathway 406) exiting the gas-gas ejector 410, through agas flow pathway 620, back to the second gas flow pathway 406 for finaldelivery to the central gas plant 106. Also, the gas flow system 400includes a flow control valve 608 fluidically coupled to the second gasflow pathway 406 to control (i.e., permit or prevent) flow of the gasphase from the second gas flow pathway 406 to the third gas flow pathway602. Also, the gas flow system 400 includes a flow control valve 616fluidically coupled to the first gas flow pathway to control (i.e.,permit or prevent) flow of the gas phase from the first gas flow pathwayto the fourth gas flow pathway 610. The flow control valves 608 and 616isolate the normal condition layout and have the flow directed to thegas-gas ejector 410.

The earlier descriptions describe a scenario at a time instant in whichthe gas-gas ejector 410 is implemented because the flow pressure of thegas phase through one of the first gas flow pathways (e.g., the firstgas flow pathway 404H) has fallen below a threshold flow pressure. Asdescribed earlier, such pressure drop can occur, for example, becausethe HP gas compressor fluidically coupled to the first gas flow pathwayis starting up or shutting down or is malfunctioning. Such pressure dropcan also occur when the flow pressure of the gas phase flowing throughthe GOSP (e.g., GOSP 402H) drops. At a later time instant, the flowpressure of the gas phase through the first gas flow pathway canincrease to at or above the threshold flow pressure. Such pressureincrease can occur, for example, because the HP gas compressorfluidically coupled to the first gas flow pathway is running optimallyat the maximum flow pressure at which the HP gas compressor is rated tooperate. Such pressure increase can also occur because the gas phase isflowing optimally through the GOSP. In such scenarios, the gas-gasejector 410 is no longer needed.

In response to determining that the flow pressure of the gas phase flowthrough the first gas flow pathway is at or above the threshold flowpressure, the controller 412 can transmit alerts similar to alertsdescribed above indicating that the gas-gas ejector 410 is no longerneeded. In response, the controller 410 can (either automaticallywithout human intervention or in response to operator input) transmitsignals to close the first flow control valve 606, close the second flowcontrol valve 614 and open the flow control valves 608 and 616. Inresponse, the portion of the gas from the second gas flow pathway 406,which was previously diverted to flow through the third gas flow pathway602, can resume flowing entirely through the second gas flow pathway 406to the central gas plant 408. Also, the gas phase from the GOSP, whichwas previously diverted to flow through the fourth gas flow pathway 610,can resume flowing entirely through the first gas flow pathway to thesecond gas flow pathway 406. In this manner, by periodically monitoringthe pressure in each first gas flow pathway, the gas flow system 400 canimplement the gas-gas ejector 410 as needed.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the followingclaims. In some implementations, features described with reference todifferent implementations can be combined into a single implementation.For example, while gas is being flowed from a network of multiple GOSPsto the central gas plant, gas can, in parallel, be flowed from a gasreservoir to the same central gas plant. In such implementations, if aflow pressure of gas phase from a GOSP drops below a threshold flowpressure, then the gas-gas ejector can be used to drive the flow of gasphase from that GOSP using either the gas phase from the second gas flowpathway that collects gas phases from all the GOSPs in the network orthe gas from the gas reservoir. In some implementations, a mixture ofgas from the second gas flow pathway and gas from the gas reservoir canbe used as motive fluid to operate the gas-gas ejector.

1. A gas flow system comprising: a gas-oil separation plant (GOSP)configured to separate multiphase hydrocarbon into a gas phase and aliquid phase; a first gas flow pathway fluidically coupled to the GOSPand configured to receive the gas phase from the GOSP and to flow thegas phase to a central gas plant at a first flow pressure; a second gasflow pathway fluidically coupled to a gas reservoir and configured toflow gas from the gas reservoir to the central gas plant at a secondflow pressure greater than the first flow pressure; a gas-gas ejectorfluidically coupled to the first gas flow pathway and the second gasflow pathway, the gas-gas ejector configured to drive gas flow using thegas from the gas reservoir as a motive gas; and a controller operativelycoupled to the GOSP and the gas-gas ejector, the controller comprising:one or more computer systems, and a computer-readable medium storingcomputer instructions executable by the one or more computer systems toperform operations comprising: determining a decrease in the first flowpressure below a threshold flow pressure; and in response to determiningthe decrease in the first flow pressure below the threshold flowpressure, operating the gas-gas ejector to operate to drive a flow ofthe gas phase to the central gas plant using gas from the gas reservoiras a motive gas.
 2. The system of claim 1, further comprising a gascompressor fluidically coupled to the first gas flow pathway, the gascompressor configured to flow the gas phase to the central gas plant atthe first flow pressure, wherein determining the decrease in the firstflow pressure below the threshold flow pressure comprises determining achange in normal operation of the gas compressor.
 3. The system of claim2, wherein the normal operation of the gas compressor comprises anoperation at a maximum flow pressure at which the gas compressor israted to operate, wherein determining the change in the normal operationcomprises determining that the gas compressor is operating at a flowpressure different from the maximum flow pressure.
 4. The system ofclaim 1, further comprising: a third gas flow pathway fluidicallycoupled to the second gas flow pathway and to a motive gas inlet of thegas-gas ejector; and a first flow control valve fluidically coupled tothe third gas flow pathway and operatively coupled to the controller,wherein operating the gas-gas ejector comprises controlling opening andclosing of the first flow control valve.
 5. The system of claim 4,wherein the first flow control valve, in an open state, is configured todivert a portion of the gas from the gas reservoir to the motive gasinlet of the gas-gas ejector, and, in a closed state, is configured tocease flow of the portion of the gas from the gas reservoir to themotive gas inlet of the gas-gas ejector.
 6. The system of claim 4,further comprising: a fourth gas flow pathway fluidically coupled to thefirst gas flow pathway and to a driven gas inlet of the gas-gas ejector;and a second flow control valve fluidically coupled to the fourth gasflow pathway and operatively coupled to the controller, whereinoperating the gas-gas ejector comprises controlling opening and closingof the second flow control valve.
 7. The system of claim 6, wherein thesecond flow control valve, in an open state, is configured, isconfigured to divert the gas phase from flowing to the central gas plantto flowing to the driven gas inlet of the gas-gas ejector, and, in aclosed state, is configured to divert the gas phase from flowing to thedriven gas inlet of the gas-gas ejector to flowing to the central gasplant.
 8. A method comprising: flowing a gas phase from a gas oilseparation plant (GOSP) to a central gas plant through a first gas flowpathway at a first flow pressure; flowing gas from a gas reservoir tothe central gas plant through a second gas flow pathway at a second flowpressure, the first gas flow pathway separate from the second gas flowpathway; while flowing the gas phase through the first gas flow pathway,determining a decrease in the first flow pressure below a threshold flowpressure; and in response to determining the decrease in the first flowpressure below the threshold flow pressure, operating a gas-gas ejector,fluidically coupled to the first gas flow pathway and the second gasflow pathway, to drive a flow of the gas phase to the central gas plantusing gas from the gas reservoir as a motive gas.
 9. The method of claim8, wherein a gas compressor fluidically coupled to the first gas flowpathway flows the gas phase to the central gas plant at the first flowpressure, wherein determining the decrease in the first flow pressurebelow the threshold flow pressure comprises determining a change innormal operation of the gas compressor.
 10. The method of claim 9,wherein the normal operation of the gas compressor comprises anoperation at a maximum flow pressure at which the gas compressor israted to operate, wherein determining the change in the normal operationcomprises determining that the gas compressor is operating at a flowpressure different from the maximum flow pressure.
 11. The method ofclaim 8, wherein operating the gas-gas ejector comprises opening a firstflow control valve that controls flow through a third gas flow pathwayfluidically coupled to the second gas flow pathway and to a motive gasinlet of the gas-gas ejector to flow a portion of the gas from the gasreservoir to the motive gas inlet of the gas-gas ejector.
 12. The methodof claim 11, wherein operating the gas-gas ejector comprises opening asecond flow control valve that controls flow through a fourth gas flowpathway fluidically coupled to the first gas flow pathway and to adriven gas inlet of the gas-gas ejector to divert the gas phase fromflowing to the central gas plant to flowing to the driven gas inlet ofthe gas-gas ejector.
 13. The method of claim 8, further comprising:while operating the gas-gas ejector, periodically monitoring a flowpressure through the first gas flow pathway; in response to periodicallymonitoring the flow pressure, determining that the flow pressure of thegas phase exceeds the threshold flow pressure; and in response todetermining that the flow pressure of the gas phase exceeds thethreshold flow pressure, flowing the gas phase to the central gas plantwhile avoiding flow of the gas phase through the gas-gas ejector. 14.The method of claim 13, further comprising, in response to determiningthat the flow pressure of the gas phase exceeds the threshold flowpressure, flowing the gas from the gas reservoir to the central gasplant while avoiding flow of the gas from the gas reservoir through thegas-gas ejector.
 15. A non-transitory computer-readable medium storinginstructions executable by one or more computer systems to performoperations comprising: receiving signals representing flow pressure of agas phase flowing through a first gas flow pathway from a gas oilseparation plant (GOSP) to a central gas plant, wherein, while the gasphase is flowed to the central gas plant, gas from a gas reservoir isflowed through a second gas flow pathway from a gas reservoir to thecentral gas plant; determining, at a first time instant, that the flowpressure is less than a threshold flow pressure; in response todetermining that the flow pressure is less than the threshold flowpressure, transmitting control signals to operate a gas-gas ejectorfluidically coupled to the first gas flow pathway and the second gasflow pathway, to drive a flow of the gas phase to the central gas plantusing gas from the gas reservoir as a motive gas.
 16. The medium ofclaim 15, wherein a third gas flow pathway fluidically couples thesecond gas flow pathway to a motive gas inlet of the gas-gas ejector,and a first flow control valve fluidically couples to the third gas flowpathway, wherein transmitting control signals to operate the gas-gasejector comprise transmitting control signals to open the first flowcontrol valve to divert a portion of the gas from the gas reservoir tothe motive gas inlet of the gas-gas ejector.
 17. The medium of claim 16,wherein a fourth gas flow pathway fluidically couples the first gas flowpathway to a driven gas inlet of the gas-gas ejector, and a second flowcontrol valve fluidically couples to the fourth gas flow pathway,wherein transmitting control signals to operate the gas-gas ejectorcomprises transmitting control signals to open the second flow controlvalve to divert the gas phase from flowing to the central gas plant toflowing to the driven gas inlet of the gas-gas ejector.
 18. The mediumof claim 17, wherein the operations comprise: determining, at a secondtime instant after the first time instant, that the flow pressure isgreater than the threshold flow pressure; and in response to determiningthat the flow pressure is greater than the threshold flow pressure,transmitting control signals to close the first flow control valve andthe second flow control valve.
 19. The medium of claim 15, whereinreceiving signals representing flow pressure of the gas phase flowingthrough the first gas flow pathway comprises receiving signals frompressure sensors fluidically coupled to the first gas flow pathway.